Re: [e2e] Opportunistic Scheduling.

ksingh@irisa.fr pointed to
> QoS control for WCDMA high speed packet data
> Hosein, P.A.
> Ericsson Wireless Commun. Inc., San Diego, CA, USA;
>

I think, there is a severe misconception in this paper, however this kind of misconception is met quite freuquently.

Kelly´s objective is the assignment of shared ressources. So, when Kelly talks about "rates", these rates are shares of shared ressources and particularly sum up to a total which is less or equal to the maximum amount of ressources.

Simple exampel:

Think of a 150 MBit/s link (is this OC/3? I always mix up the numbers), than this can be shared among three flows which are assigned for instance

- 20 MBit/s
- 80 Mbit/s
- 50 MBit/s

What we talk about in mobile networks are _code_ _rates_, and even this is simplified because there might be some kind of dynamic channel adaption by a per time slot choice of the symbol set.

So, although some flow may be scheduled "at a rate" 30 kbit/s and some other flow may be scheduled "at a rate" 60 kbit/s, both flows will typically (in HSDPA like systems) occupy _the_ _same_ _amount_ of ressources because the radio blocks have the same length in symbols, only the information words differ in lenghts depending on the actual coding scheme / puncturing scheme.

Hence, when we use code rates, even the boundary conditions in Kelly´s model can not be met in the original manner but would have to be adapted to the different meaning of "rate".

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Particularly, I once again emphasize that a stream scheduled "at a small rate", i.e. code rate does _not_ occupy less ressources than one scheduled "at a high rate".

So, simply spoken: I severely doubt Hoseins rationale.

Another point which is not convincing is, that in Hoseins paper the "actual vector of average rates" is made to follow an "optimal vector of rates" which is itself a moving target and may be subject to severe fluctuation.

Perhaps, there is a severe flaw in my way of thinking, but at the moment, my doubts in the "opportunistic scheduling" algorithm as it is in use today become not lesser but bigger.

Detlef

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